Kidding aside, the challenge decks (DC's) are official ICE decks, meant for introducing new players to the game, hence nobody has really seen the need to improve them. If you feel they are unbalanced, seems to me you are ready for the next step and play a constructed deck...

But, for people with a very limited collection, it could be a nice idea to take CD's as a start to make something better.

nb. there are people who have done quite well with the Alatar or Radagast CD in a normal tournament.